Well for starters, you have alot of temp differential, for example I see a 15 degree temp differential. I try to keep temps tighter than that. You have 15 degree DIF, thats alot, I work with a 7 degree DIF at one of the medical grows I’m working.
Observation
Nighttime temp is out of spec That can cause phosporous problems.
I see purple/red stems could be N,P,
Yellowing of veins
Lower foilage “draw” as I call it could be from shading but looking at other things. It looks deficient, the leaves have chlorosis, but do not have green veins.
Tip dieback and claw.
Top foilage looks ok.
How you got there…
N is needed in first weeks of stretch, now its showing low N.
P is easily blocked, or locked up, or used up. PK is immobile in soil.
Lower shaded foilage can fade, the rest of the plant can draw from these leaves, looking like fade. I even see it in hydro. Fan leaf drop does happen even in perfectly fed plants.
Increased need of P during flower.
Nighttime temp is out of spec That can cause phosporous problems.
Possible fix:
-Nighttime temps with less DIF and temps closer to normal 65+ Verify soil temps with probe or non contact IR thermometer. Get into proper range.
-Foliar feed, use a very dilute solution of macros’ NPK and I lean towards nitrate based stuff, mainly for solubility.
And you can use a surfactant with it, spray the bottoms of the leafs, prior to lights out or before lights on. Less of a cuticle to worry about penetrating and the stomata are open. you can use soaps for a surfactant, but typical dish soap isn’t really designed for wetting. Spreader, sticker wetting agents are relatively cheap. Be careful of burn, you could try a typical off the shelf solution, or some type of organic formulation, be careful of what you use if organic, fungal or PM outbreak could occur due to lower temps at night. Avoid application to budsites,
-Inoculant using microbes, powdered molasses and humics and fulvics to possibly unlock PK. I hate to plug any product, but “Recharge” works fairly well (Realgrowers.com) Or a light topdressing of EWC and compost. Topdressing is a very easy way to help soil biology and chemistry and tilth.
-Fish based or protein based fertilizers or products with high nitrogen to help bump the chemistry in the right direction, I am partial to fish… They have alot of microbe activity, and you can find balanced fish fertilizers.
Test soil if possible.
Just some thoughts… No warranty expressed or implied.